Gasping for Air

I don't know what is causing it but i am having problems breathing. Some have suggested that it is stress related, or some sort of anxiery attack. I have been to a doctor (well a couple actually) and they have told me that i am fine physically.

It just shits me that sometimes i suddenly start trying to pull deep breaths that I cannot let go of. I am wondering if I am getting stressed about the run on the weekend. I have not done as much training as I should have, and although i feel fit i am probably remembering the failure that I had at the Corp games in March.

At that run I collapsed and did not even finish the race. It was only 10km, and this one is 21km. I guess I will find out on sunday....